Patent GB-465367-A (GB)
Title: Improvements in or relating to milling machines for copying and reproducing
IPC: B23Q35/18
Filed: 1935-12-31
Abstract: 465,367. Fluid-pressure servomotor-control systems. STEVENS, A. H. (Cincinnati Milling Machine Co.) Dec. 31, 1935, No. 36068. [Class 135] [Also in Group XXII] A pattern-controlled milling-machine has slides movable in directions normal to each other and actuated by fluid-pressure motors controlled by a directional control valve which determines the resultant feed between cutter and work, the tracer mechanism comprising a rotatable head which has the tracer button universally mounted thereon, and is automatically rotated to maintain the radius arm perpendicular to the pattern' at the point of contact, the deflection of the tracer acting on the directional control valve so that the feed is always perpendicular to the radius arm. The principle of the tracer control is shown in Figure 18 wherein a cutter having a centre at 13 acts on a work-piece 11 mounted adjacent the pattern 10. The line Y Y<1> passes through a point 12 maintained in fixed relation to the cutter centre, and is perpendicular to the pattern. If the point 12 moves around a path 14 and the line Y Y<1> is maintained perpendicular to the pattern surface the cutter will correctly reproduce the pattern. Thus the tracer could be a short arm 12, 15 terminating in a tracing knife edge and if the length of this arm is variable the tracer could be used for cutters of different diameters. Or a tracer button represented by the circle 18 and having a centre at 17 when undeflected, could be employed. When the tracer centre is at 19 i.e. the tracer is in contact with the pattern surface and is deflected by the distance 17-19 it is in a neutral position wherefrom it deflect either towards or away from the pattern centre. When the tracer reaches the point 20 it moves towards the pattern centre and its deflection decreases and this decrease is used to re-establish the required perpendicular relationship of the radius arm to the pattern. For this purpose the tracer is mounted in a rotary head having its axis at 12, the head being rotated in one or other direction until the line Y Y<1> resumes the perpendicularity to the surface 21. In the machine shown the cutter and tracer rotate about fixed axes and feed movements are provided for the work and pattern along the line X X<1> perpendicular to line Y Y<1> which is itself always perpendicular to the pattern contour. The resultant direction of feed is thus continually changing, the work and pattern being mounted on compound slides having the required relative movements. In practice the centre of the tracer button is slightly offset from axis Y Y<1> as shown in Fig. 16. The tracer head 25, Figs. 6 and 7, secured to the rotatable member 26 has a dovetail diametral guideway 30 in which the tracer body 31 is adjusted by a graduated micrometer screw 33. A ring 40 supports on ball-bearings a flanged disc 41 carrying the shank 45 of the tracer button 48. The centre of member 41 receives a ball contacting a disc 51 on a vertical tracer arm 52. Thus axial pressure on the button imparts corresponding axial movement to the tracer arm. Also radial pressure on the button tilts the disc 41 about a point on its periphery and also produces axial movement of the tracer arm. The adjustment by the screw 33 enables the tracer to be reset when the cutter becomes worn or to be set so that the cutter leaves the work oversize for subsequent finishing to true size. Further the tracer may be set relatively to the cutter as in Fig. 35 so that a punch A may be cut to the pattern of a die B or vice versa. The tracer head or button may be of different shapes but should preferably have an arcuate surface of at least an angle of 90‹. The size of the tracer in relation to the cutter is chosen according to the type of work to be performed. The power means controlled by the tracer is so arranged that during increase in the tracer deflection the rate of rotation of the tracer head decreases from a maximum to zero while at the same time the feed rate along axis X X<11> increases from zero to a maximum. This condition exists between a minimum tracer deflection and the neutral position (centre at 19, Fig. 18). Further deflection of the tracer beyond this point decreases the feed rate from maximum to zero and increases the rate of rotation of tracer head in the opposite direction from zero to maximum. When the tracer is free of the pattern the feed is a maximum and the tracer head is not rotated. In starting the machine the axis X .. X<1> is pointed towards the pattern, Fig. 10, the undeflected tracer centre being at 17. Continued movement in the direction of X .. X<1> causes the tracer button to be deflected by an amount 60, Fig. 11, and to reach the position wherein the feed rate is zero and the rotation a maximum. This rotation causes the tracer head to assume the neutral, Fig. 12, position with increased feed and zero tracer head rotation. As the feed continues along X .. X<1> further deflection of the tracer will ensue and the tracer rotation is accelerated in the reverse direction with decreasing feed. Thus the feed causes further deflection and the rotation decreased deflection of the tracer until an equilibrium is established with the tracer and cutter positioned as in Fig. 16 with the feed direction X .. X<1> parallel to the work surface as in Fig. 18 and the tracer in neutral position. In the machine embodiment the column 63 has guideways for a knee 65 carrying a saddle 67 and table 68 the latter carrying the work and pattern beneath the cutter 69 and tracer 48 respectively. The motor 72 drives a shaft 73 geared to the cutter spindle at variable speeds and a vertical shaft 77 geared to the shaft 73 extends into the pedestal 79 and drives a coolant pump for the cutter. The shaft 77 also drives a pump 82 of either constant or variable displacement. The hydraulic system is shown in Fig. 17. The pump output flows through line 85 to a double throttle valve 87 having ports 90, 91 the former being connected to a balancing valve 96 which acts as described in U.S.A. Specification 2,005,732 to distribute the flow between ports 90, 91. The throttle valve is adjusted by a cam lever 94. The power fluid flows from port 91 to a distributer valve 108 whose plunger is connected to the arm 52 of the tracer mechanism, a spring 112 normally serving to maintain the tracer in undeflected position. This valve is connected to a valve 117 and also to balancing valves 121, 124. The port 113 of distributer valve 108 supplies the motors actuating the table and saddle and the ports 114, 115 supply fluid for the tracer head rotation the direction of which is controlled by a reversing valve 147. In the free tracer position all the fluid is delivered to channel 138 to feed the slides at maximum rate. When the tracer has been deflected by the pattern to the engagement position the plunger 111 moves upwardly and fluid flows in the line 113 and shifts valve 117 to the left. When this occurs fluid passes into the line 144 to rotate the tracer head motor at maximum rate. Further the port 137 is connected to line 126 to operate the work slides at minimum rate. As the tracer deflection increases the plunger 111 move upwards and further opens port 113 leading to line 126 so that the feed movement increases and the tracer head rotation decreases. In the neutral tracer position the feed is a maximum and the tracer head rotation is. zero. From this position movement in either direction causes tracer head rotation in one direction or the other and decreased feed movement. The tracer head motor, Fig. 8, comprises a rotary valve member 154 controlling the flow from the ports 145, 146 shown diagrammatically on Fig. 17 to channels leading to cylinders 166, 167 and 168. An operating knob 159 sets the valve 154 to determine the initial direction of rotation. Each cylinder carries a piston 169 engaging an eccentric cam 170 carrying an antifriction ring 171. The cams are splined on a shaft 172 carrying a spiral gear 173 meshing with a similar gear 174 on the tracer head. This mechanism also operates the rotary directional control valve 140 which has ports 176-179 connected to a series of balancing valves 184, 187 mounted in a common casing and separated by partitions. The lines 180, 183 are also connected to the hydraulic cylinder which moves the work in two directions in its plane the cylinder 189 giving the N-S movement and cylinder 192 the E-W movement. If pressure is admitted to one end of one cylinder say to port 190 movement in the " North " direction will occur and the port 191 is connected to exhaust. The other cylinder is hydraulically locked. If for instance a S-W movement is required, pressure is admitted to two cylinders (ports 191, 194) at the same time the correct distribution of fluid between the cylinders being given by the balancing valve 187 which takes up a position which balances the pressure between the S an W lines and maintains proportionate flows thereto as established by the directional control valve 140. The balancing valves operate as described in U.S.A. Specification 1,999,834. Similarly valve 186 balances the pressure distribution in ports 190, 194 for a N-W movement. The hydraulic cylinder construction for the work movement is shown in Fig. 4. The piston 188 is rigidly mounted and the cylinder 189 constitutes the moving member. A longitudinal bore 235 conveys fluid to the left end of the cylinder and a tube 237 passing through this bore conveys fluid to the right-hand end. The table cylinder is fixed and the table moves with the piston rod when fluid is admitted to one of the ports 193, 194. The directional control valve 140 divides the flow among the four supply lines of the slide motors in such a way that one rotation of the valve moves the work support through 360‹ relative to the tracer. For each 90‹ position of member 26 which forms the rotatable element of the valve 140, a segmental groove such as 256, Fig. 26, in the member 26 will b